To manufacture a thin disc such as a semiconductor wafer, an elongated billet of semiconductor material is cut into very thin slices, about 3/4 mm in thickness. The slices or wafers of semiconductor material are then lapped and polished by a process that applies an abrasive slurry to the semiconductor wafer's surfaces. A similar polishing step is performed to planarize dielectric or metal films during subsequent device processing on the semiconductor wafer.
After polishing, be it during wafer or device processing, slurry residue conventionally is cleaned from wafer surfaces via submersion in a tank of sonically energized cleaning fluid, via spraying with sonically energized cleaning or rinsing fluid, or via a scrubbing device which employs brushes made from bristles, or from a sponge-like material, etc. Although these conventional cleaning devices remove a substantial portion of the slurry residue which adheres to wafer edges, slurry particles nonetheless remain and produce defects during subsequent processing. Specifically, subsequent processing has been found to redistribute slurry residue from the wafer edges to the front of the wafer, causing defects.
A number of devices have been developed to improve wafer edge cleaning. Most of these devices are employed as a separate step following major surface cleaning or scrubbing. However, a few scrubbing devices have been developed that can simultaneously scrub both the major and edge surfaces of a wafer. One such device is shown in the side elevational view of FIG. 1. The scrubbing device 11 of FIG. 1 comprises a pair of PVA brushes 13a, 13b. Each brush comprises a plurality of raised nodules 15 across the surface thereof, and a plurality of valleys 17 located among the nodules 15. The scrubber 11 also comprises a platform 19 for supporting a wafer W and a mechanism (not shown) for rotating the pair of PVA brushes 13a, 13b. The platform 19 comprises a plurality of spinning mechanisms 19a-c for spinning the wafer W. During scrubbing a fluid supply mechanism F, such as a fluid source coupled to a plurality of spray nozzles, supplies fluid to both major surfaces of the wafer, flushing dislodged particles and cleaning residue from the major surface of the wafer and rinsing brushes 13aand 13b. Preferably, the pair of PVA brushes 13a, 13b are positioned to extend beyond the edge of the wafer W, so as to facilitate cleaning the wafer's edges. This mechanism further employs a separate edge brush 21, which is driven by a separate motor (not shown), that causes the edge brush 21 to rotate. The edge brush 21 fits over the edge of the wafer W as shown in FIG. 1, providing more effective wafer edge cleaning.
Although the edge brush 21 addresses the need to clean slurry residue from wafer edges, it does so at the expense of increased scrubber complexity and cost, and the requirement of frequent edge brush replacement because of excessive mechanical wear. Often, megasonic wafer cleaning within a submersion tank is preferred to scrubber type cleaning, such as when it is desirable to alter the chemistry of the cleaning solution as the PVA brushes commonly used for brush scrubbing have limited chemical compatibility (e.g., to make the wafer hydrophobic or hydrophilic). In these instances, the use of a conventional edge scrubber following megasonic cleaning significantly increases wafer cleaning time, reducing productivity, and thereby increasing the cost of each wafer unit processed.
Accordingly, the field of semiconductor wafer processing needs an improved megasonic cleaner that will simultaneously clean both the major surfaces and the edge surfaces of a wafer, and that will do so with minimal additional components so as to satisfy the ever present demand for reduced processing costs.